Dowding and Doll V-4 gear hobber

[Pete.]

The three sets of gears:

This arrangement is how you set the gears according to how many teeth are on the gear you want to cut. It's the same regardless of whther it's a spur gear, a helical gear or a wormwheel.

This set of gears determines the feed rate for cutting spur gears. Since the teeth are square across the gear you only need to set the feed rate you require to get a nice finish on the tooth, and to give good tool life. The square drive end pokes out through the casing and allows for a handle for moving the feed slide manually:

These are the differential gears. They are arranged (using fancy calculations) to turn the gear blank at such a rate that it allows for the extra rotation required to time to hob and blank correctly when cutting helical gears. This is something I have to learn to do.

There's a warning in the manual that you must be sure to disengage the feed gears before engaging the differential gears, or serious damage will result. It's a bit like putting your car in 1st and second gear at the same time (if you could) - you're going to mash something up. I suspect that someone has done just this because one of the feed gears has damage in several places:

Thankfully, the damage seems restricted to a few teeth on one gear. I can re-make this one easily enough.

 

[Pete.]

Stack of change gears. There are four different sizes of gear. 2mod for the hob speed gears, 1.5mod for the input gears for the index banko, 1.25 mod for the index change gears and 1 mod for the feed and differential change gears.

Inside the electrical panel. Very basic, an on-off pushbutton switch for the pump, a fwd/rev switch for the motor and a pair of momentary buttons to operate the motor contactor.

This makes me very happy. The 1/2" arbor is removable and fits on a shallow taper with a 5/16"UNF drawbar. This means that I can make a new taper and allows me to use my extensive collection of 10mm hobs, plus any other size hob I might find.

BTW that arbor was very very stuck in there Took 4 tonnes on my press to release and buckled the drawbar so I have to make a new one.

 

[Pete.]

Oh, BTW I did get the machine to a place where I could power it up with the motor, but I decided against it. Some of the slides and movements were very gummed up from lack of use and I was worried that the same might be true of the multitude of gearboxes and shaft bearings. I want to go right through the machine lubing up and de-gumming everything before running it under power so I don't end up tearing up a plain bearing.

 

[Shiny Steve]

Good to see it back together Pete, the overall condition looks really nice.

 

[Stueeee]

First bit to go is the isolator. I always remove these becaus eI just use a 3 pin plus so if I want to isolate something I pull the plug out

If anyone wants it put your hand up.

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@pete My hand is up if that isolator is still available.

You made great time collecting that. When I saw the advert I googled the postcode; somewhere near Preston IIRC. That machine looks to really versatile and a real great find.

 

[Pete.]

@pete My hand is up if that isolator is still available.

You made great time collecting that. When I saw the advert I googled the postcode; somewhere near Preston IIRC. That machine looks to really versatile and a real great find.

Sure thing Stu I got a couple of them you can have.

 

[Stueeee]

Thanks for that, will be ideal for the J&S grinder that I'm currently wrestling into the rear workshop as part of my machine tool Tetris project.

 

[Pete.]

Here's a handy feature that both my hobbers have. The two bolts in the middle are pinch bolts for the very finely bored housing. They allow you to move the spindle quill in and out (you can see it's quite a bit 'out' in the pic as the gears are mis-aligned) a certain amount to balance the wear on the hob. A tiny bit of pinch is required to hold the spindle in place, if you use too much it deforms the quill and binds the spindle. Just like my Mikron, the spindle is plain hardened steel running on a plain bore with generous grease grooves.

Spot the iffy-looking countersunk screw holding the far gear. Someone put the washer on backwards - the other side is countersunk, so I turned it around

 

[fizzy]

It's back together. There's still a lot of cleaning to do, and oiling too as well as a bit of repair

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Here's the clever end, 3 entirely separate sets of adjustable gear trains:

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And more fancy gubbins inside:

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The red bits are flakes of paint where we took it apart.

Sorry but made me think of this

 

[fizzy]

And I am very very jealous and want one. Base reminds me a bit of my Elliott 10m.
Just think how much a machine like that would cost new

 

[Martin Hocking]

Wow! Pete, that machine couldn’t have found a better home. Lovely to see.

I’m looking forward to plenty of “oh I never knew that…” moments in this thread. Already had a few!

 

[minimutly]

I could think of one...

 

[Pete.]

I could think of one...

If it was only for cutting spur gears I would have passed it over, but I really wanted a machine that could cut helicals.

 

[minimutly]

You seen this?

Pardon our interruption...

 

[fizzy]

You seen this?

Pardon our interruption...

I thought that is a great bargain - then I saw they are £120 EACH

 

[Pete.]

Yeah that ad's been running several years. I actually have the full list.

 

[Pete.]

They were clever buggers back in the day. I guess there are still some now

Big taper = full hard
Small taper = full hard
Shoulder/spanner flat = full hard
Arbor shank = full hard

Thread - not hard at all.

 

[Pete.]

So, this evening I sorted through the piles of gears.



I have:
4no MOD2 hob speed gears
5no MOD2 ratio/reversing gears
36no MOD1.5 index gears
10no MOD1 feed change gears
59no MOD1 differential change gears

Which is exactly what should be with the machine. One of the gears (90T feed gear) has several damaged teeth but contrary to what I said befor eI don't think it's from engaging the direct feed drive and differential drive together but simply a matter of the gears being engaged too tightly on the banjo. Luckily it's a mod1 gear and the machine came with a mod1 hob so I can make a replaement.

I also discovered why the differential gears are called differential gears - they turn a differential:

I'm still trying to wrap my head around this but it seems that one side of the diff is driven at normal feed-rate speed and the other side is driven by the worm which adds in the bit extra you need to advance the blank according to the helical angle, and combined they'll cut the teeth at an angle.

 

[ukracer]

I thought that is a great bargain - then I saw they are £120 EACH

Snap....I thought the same..lol

 

[Pete.]

Spent a couple of hours tonight doing my cleaning and oiling rounds. To get proper access I removed the hob spindle head, the collet block and the support arn and tailstock. I cleaned up the table slideway, removed the lock, cleaned all the gummy dried oil off it and put it back together, then I cleaned the hob carrier slideways so they all moved nice and smooth. Note all of the slideways are hand scraped and still show all the scraping.



Here's the revolving table, the bit that holds and turns the collet block for the gear blank arbor



Here's the drive gear and the bronze driven gear for the spindle. No wear to see.





The downfeed handle slides in and out and is held out by a spring. It was all gummed up but now it's working just fine.



Down under the table there's an inspection cover. Behind it is a spring cover that closes an oiling hole which you fill with oil for the worm drive. I woner if anyone had bothered to ever fill it up but I have done it now.



Finally I measured the collet, to try to determine the type. Well, it's typical b@stard size British - 19/32" - 20tpi, which is exceeedingly close to 15mm - 1.25mm pitch.

That's about it for now I am confident that it's lubed up well enough to actually go into use.